U.S. patent number 9,722,273 [Application Number 14/476,851] was granted by the patent office on 2017-08-01 for fuel cell system components.
This patent grant is currently assigned to BLOOM ENERGY CORPORATION. The grantee listed for this patent is BLOOM ENERGY CORPORATION. Invention is credited to Arne Ballantine, Martin Perry.
United States Patent |
9,722,273 |
Perry , et al. |
August 1, 2017 |
Fuel cell system components
Abstract
A fuel cell stack module includes a plurality of fuel cell
stacks, a base supporting the plurality of fuel cell stacks, and a
metal shell located over the base and the fuel cell stacks. The
metal shell contains an integrated heat exchanger.
Inventors: |
Perry; Martin (Sunnyvale,
CA), Ballantine; Arne (Palo Alto, CA) |
Applicant: |
Name |
City |
State |
Country |
Type |
BLOOM ENERGY CORPORATION |
Sunnyvale |
CA |
US |
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Assignee: |
BLOOM ENERGY CORPORATION
(Sunnyvale, CA)
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Family
ID: |
40382479 |
Appl.
No.: |
14/476,851 |
Filed: |
September 4, 2014 |
Prior Publication Data
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Document
Identifier |
Publication Date |
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US 20150140468 A1 |
May 21, 2015 |
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Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
Issue Date |
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12222736 |
Aug 14, 2008 |
8852820 |
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60935471 |
Aug 15, 2007 |
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Current U.S.
Class: |
1/1 |
Current CPC
Class: |
H01M
8/04022 (20130101); H01M 8/04007 (20130101); H01M
8/04074 (20130101); H01M 8/2475 (20130101); H01M
8/04268 (20130101); H01M 8/249 (20130101); Y10T
29/49108 (20150115); Y02E 60/526 (20130101); H01M
2008/147 (20130101); H01M 2008/1293 (20130101); Y02E
60/50 (20130101) |
Current International
Class: |
H01M
8/24 (20160101); H01M 8/2475 (20160101); H01M
8/04223 (20160101); H01M 8/04014 (20160101); H01M
8/04007 (20160101); H01M 8/249 (20160101); H01M
8/04 (20160101); H01M 8/124 (20160101); H01M
8/14 (20060101) |
References Cited
[Referenced By]
U.S. Patent Documents
Foreign Patent Documents
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2653441 |
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Jan 2008 |
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CA |
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198 22 697 |
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Oct 1999 |
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DE |
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0 398 111 |
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Nov 1990 |
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EP |
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0817298 |
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Jan 1998 |
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EP |
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0977294 |
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Feb 2000 |
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EP |
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1501146 |
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Jan 2005 |
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EP |
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62-115673 |
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May 1987 |
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JP |
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5-47408 |
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Feb 1993 |
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JP |
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2005-044727 |
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Feb 2005 |
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JP |
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2006-032290 |
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Feb 2006 |
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JP |
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2006-221854 |
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Aug 2006 |
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JP |
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WO94/18712 |
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Aug 1994 |
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WO |
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WO2004/013258 |
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Feb 2004 |
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WO |
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WO2004/092756 |
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Oct 2004 |
|
WO |
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WO2004/093214 |
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Oct 2004 |
|
WO |
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WO2006/048429 |
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May 2006 |
|
WO |
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Other References
Austin, "Cell and Stack Construction: Low-Temperature Cells," Fuel
Cells: A Review of Government-Sponsored Research, 1950-1964, NASA
SP-120, pp. 101-102, (1967). cited by applicant .
"Low Cost, Compact Solid Oxide Fuel Cell Generator," (Technology
Management Inc.). cited by applicant .
"Low Cost, High Efficiency Reversible Fuel Cell (and Electrolyzer)
Systems," (Technology Management Inc.), Proceedings of the 2001 DOE
Hydrogen Program Review NREL/CP-570-30535, pp. 1-7, (2001). cited
by applicant .
Milliken et al., "Low Cost, High Efficiency Reversible Fuel Cell
Systems," Proceedings of the 2002 U.S. DOE Hydrogen Program Review,
NREL/CP-610-32405, pp. 1-14, (2002). cited by applicant .
Mitlitsky, et al., "Regenerative Fuel Cells for High Altitude Long
Endurance Solar Powered Aircraft," Intersociety Energy Conversion
Engineering Conference (IECEC), UCRL-JC-113485, pp. 1-8, (Jul. 28,
1993). cited by applicant .
Mitlitsky et al., "Unitized Regenerative Fuel Cells for Solar
Rechargeable Aircraft and Zero Emission Vehicles," 1994 Fuel Cell
Seminar, UCRL-JC-117130, pp. 1-7, (Sep. 6, 1994). cited by
applicant .
Ruhl, "Low Cost Reversible Fuel Cell System," Proceedings of the
2000 U.S. DOE Hydrogen Program Review, NREL/CP-570-28890, pp. 1-9,
(Jun. 15, 2000). cited by applicant .
"Small, Ultra Efficient Fuel Cell Systems," (Technology Management
Inc.), Advanced Technology Program ATP 2001 Competition, pp. 1-2,
(Jun. 2002). cited by applicant .
Anonymous, Presentation of the LabView-based software used in the
Fuel Cell Technologies Testing System. Internet Article, Jul. 15,
2004,
http://web.archive.org/web/20040715025135/fuelcelltechnologies.com/Suppor-
t/Downloads/Tutorial.pdf. cited by applicant .
Hamburger, R. O., et al., "LabView DSC Automates Fuel Cell Catalyst
Research", Nov. 4, 2004,
http://web.archive.org/web/20041104200039/http://bloomy.com/newsletters/f-
uelcellresearch.pdf. cited by applicant .
International Preliminary Report on Patentability,
PCT/US2010/041238, Jan. 19, 2012, 6 pages. cited by applicant .
International Search Report & Written Opinion,
PCT/US2010/041238, Mar. 2, 2011, 9 pages. cited by applicant .
Office Action issued in Japanese Application No. 2008-552342,
mailed on Aug. 28, 2012. cited by applicant .
Office Action and Supplemental European Search Report issued in
European Application No. EP 07 71 6860, mailed Jun. 10, 2014, 12
pages. cited by applicant.
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Primary Examiner: Apicella; Karie O'Neill
Attorney, Agent or Firm: The Marbury Law Group PLLC
Parent Case Text
CROSS-REFERENCE TO RELATED PATENT APPLICATIONS
The present application is a continuation of U.S. application Ser.
No. 12/222,736, filed Aug. 14, 2008, which claims benefit of U.S.
Provisional Application No. 60/935,471, filed Aug. 15, 2007, which
is incorporated herein by reference in its entirety.
Claims
What is claimed is:
1. A fuel cell stack module, comprising: a shell having a plurality
of doors; a support disposed inside the shell and having a vertical
mounting surface; and a plurality of solid oxide fuel cell stacks
horizontally mounted on the vertical mounting surface of the
support in vertically separated layers inside the shell such that
the plurality of horizontally mounted fuel cell stacks have a
stacking direction that extends perpendicular to a major surface of
one of the plurality of doors.
2. The module of claim 1, wherein the solid oxide fuel cell stacks
are mounted on the support using one or more rails.
3. The module of claim 1, wherein the support comprises a central
column having the mounting surface and containing an integrated
heat exchanger.
4. The module of claim 3, wherein the plurality of solid oxide fuel
cell stacks comprise an annular array of internally manifolded
solid oxide fuel cell stacks surrounding a central axis in the
central column.
Description
BACKGROUND OF THE INVENTION
The present invention relates generally to the field of fuel cell
systems and more particularly to a fuel cell system components.
Fuel cells are electrochemical devices which can convert energy
stored in fuels to electrical energy with high efficiencies. High
temperature fuel cells include solid oxide and molten carbonate
fuel cells. These fuel cells may operate using hydrogen and/or
hydrocarbon fuels. There are classes of fuel cells, such as the
solid oxide regenerative fuel cells, that also allow reversed
operation, such that oxidized fuel can be reduced back to
unoxidized fuel using electrical energy as an input.
SUMMARY
A fuel cell stack module includes a plurality of fuel cell stacks,
a base supporting the plurality of fuel cell stacks, and a metal
shell located over the base and the fuel cell stacks. The metal
shell contains an integrated heat exchanger.
BRIEF DESCRIPTION OF THE DRAWINGS
FIG. 1A is a three dimensional cut away view of a fuel cell module
of an embodiment of the invention with a shell removed. FIG. 1B is
a schematic side cross sectional view of the module of FIG. 1A.
FIG. 1C is a top view of the module of FIG. 1A. FIGS. 1D, 1E, 9 and
10 are top views of the module according to alternative embodiments
of the invention.
FIGS. 2A, 2B and 5 are schematic diagrams of the components and
fluid flow directions of fuel cell systems of embodiments of the
invention.
FIG. 3 is a computer simulation of a plot heat exchanger heat duty
versus temperature for a heat exchanger according to an embodiment
of the present invention.
FIG. 4 is schematic diagram of the zones and fluid flow directions
of the heat exchanger according to an embodiment of the present
invention.
FIGS. 6 and 7 are three dimensional cut-away views of two types of
multi-stream plate heat exchangers that may be used in embodiments
of the present invention.
FIG. 8 is a schematic three dimensional view of a modular fuel cell
system according to one embodiment of the invention.
FIGS. 11 and 15B are schematic side cross sectional views of
modules of alternative embodiments of the invention. FIGS. 15A and
15D are top views and FIG. 15C is a three dimensional view of the
module of FIG. 15B.
FIG. 12 is a partial side view of a flange connection of an
embodiment of the invention.
FIGS. 13A, 13B, 14A and 14B are three dimensional views of
interconnects of embodiments of the invention.
DETAILED DESCRIPTION OF THE EMBODIMENTS
The first embodiment of the invention provides a fuel cell stack
module 1 which is illustrated in FIGS. 1A, 1B and 1C. The module 1
contains a base 3, which comprises a chamber 5 and a base plate 7
above the chamber 5 which provides an upper surface of the base 3.
The base 3 may have a cylindrical shape, with a flat upper surface
and a circular cross section, as shown in FIGS. 1A and 1C. However,
the base 3 may have any other suitable shape, such as a square,
rectangular, polygonal, oval or irregular cross section. The base
plate 7 may comprise a separate component which is attached to the
chamber 5 or the base 3 may comprise a unitary component in which
the chamber 5 comprises its interior volume and the base plate 7
comprises its upper surface. As will be described below, one or
more heat exchangers 13 can be located inside the chamber 5.
As shown in FIGS. 1A-1C, each fuel cell stack module 1 includes at
least one fuel cell stack column 9 (which will be referred herein
as a "stack" for simplicity) and an outer shell 11. The shell 11
can have any suitable shape, such as a dome, a covered cylinder
(including a cylinder with a flat top cover or a cylinder with a
dome shaped cover (which helps to reduce thermal stress)), a cube
or a three dimensional rectangle, for covering the stack(s) 9. The
shell 11 is shown in FIG. 1B and its location from the top is shown
as a dashed line in FIGS. 1C-1E. For example, two or more stacks 9,
such as four to twelve stacks 9 may be located under the shell 11.
The stacks 9 are preferably stacked vertically under each shell 11.
If desired, the vertically stacked fuel cell stacks 9 may be
provided in a cascade configuration, where the fuel exhaust stream
from one stack is used as the inlet fuel stream for an adjacent
stack, such as, for example, a cascade to and from modules in the
same column.
The stacks 9 may comprise any suitable fuel cells. For example, the
fuel cells may comprise solid oxide fuel cells having a ceramic
oxide electrolyte. Other fuel cell types, such as PEM, molten
carbonate, phosphoric acid, etc. may also be used. The stacks 9 may
comprise externally and/or internally manifolded stacks. For
example, the stacks may be internally manifolded for fuel and air
with fuel and air risers extending through openings in the fuel
cell layers and/or in the interconnect plates between the fuel
cells. Alternatively, as shown in FIGS. 1B and 1C, the fuel cells
may be internally manifolded for fuel and externally manifolded for
air, where only the fuel inlet and exhaust risers extend through
openings in the fuel cell layers and/or in the interconnect plates
between the fuel cells. The fuel cells may have a cross flow (where
air and fuel flow roughly perpendicular to each other on opposite
sides of the electrolyte in each fuel cell), counter flow parallel
(where air and fuel flow roughly parallel to each other but in
opposite directions on opposite sides of the electrolyte in each
fuel cell) or co-flow parallel (where air and fuel flow roughly
parallel to each other in the same direction on opposite sides of
the electrolyte in each fuel cell) configuration. Each stack 9 may
have one fuel inlet and outlet, as will be described in more detail
below. However, if desired, each stack 9 may have several fuel
inlets and outlets along its height. In that case, each stack 9
contains plural sub-stack units (i.e., each stack column 9 contains
separate sub-stacks).
As shown in FIGS. 1C, 1D and 1E, the plurality of angularly spaced
fuel cell stacks 9 are arranged to form an annular array (i.e., a
ring-shaped structure) about a central axis of the module. It
should be noted that the term "annular array" is not limited to an
array having a circular perimeter, which is shown in FIG. 1D. For
example, the array may have a hexagonal or rectangular (square)
perimeter, as shown in FIGS. 1C and 1E, respectively, or elliptical
perimeter, which would provide a narrower system, which could then
more easily fit in a standard shipping container. The fuel cell
stacks 9 have a stacking direction extending parallel to the
central axis of the module 1. Preferably, but not necessarily each
of the stacks 9 has a rectangular cross section. The stacks 9 are
isolated from each other using ceramic or other insulating spacers.
While stacks 9 arranged as an annular array are preferred, any
other stack 9 layout which would fit within the shell 11 may be
used, such as an arc layout (i.e., a portion of a ring) or a grid
layout (e.g. 20 stacks, 4 rows by 5 columns) for example.
The shell 11 may have any suitable configuration. For example, the
shell 11 may have a cylindrical configuration. However, the shell
11 may have a polygonal or oval horizontal cross section and/or it
may have a tapered rather than flat upper surface. The shell may be
made of any suitable thermally insulating or thermally conductive
material, such as metal, ceramic, etc.
The stack(s) 9 and the shell 11 are removably positioned or
removably connected to an upper surface (such as the base plate 7)
of the base 3. Preferably, each fuel cell stack 9 and the shell 11
are separately removably connected to the upper surface 7 of the
base 3. In this case, the shell 11 may be easily removed from the
upper surface 7 of the base 3 without removing the stack(s) 9 under
the shell 11. Alternatively, if the shell 11 contains a door or a
hatch, then the stack(s) 9 under the shell 11 may be easily removed
through the door or hatch without removing the shell 11.
The term "removably connected" means that the stack(s) 9 and/or the
shell 11 are connected to the upper surface 7 of the base 3 in such
a way as to be easily removed for repair or servicing. In other
words, "removably connected" is an opposite of "permanently
connected". For example, the stacks 9 and/or the shell 11 are
removably connected to the upper surface 7 of the base 3 by at
least one of a snap fit connection, a tension fit connection, a
fastening connection or a slide rail connection. An example of a
snap fit connection is a bayonet type connection in which one or
more prongs which hold a component in place by hooking into an
opening are pressed inward or outward to unhook them from the
opening. An example of a tension fit connection is where a
component, such as a stack 9 or a shell 11, is pressed into an
opening or groove in the surface 7 of the base 3 which has the
about same size as the cross section of the stack 9 or the shell 11
such that tension holds the stack or the shell in the opening or
groove. An example of a fastening connection is connection by a
fastener, such as a bolt or a clip, which can be removed by service
personnel. An example of a slide rail connection is a drawer or
dove tail type connection, such as a groove in the upper surface 7
of the base 3 into which a protrusion in the stack 9 can be slid
into, or a groove in the bottom stack 9 plate into which a
protrusion in the upper surface 7 of the base 3 can be slid into.
An example of a permanent connection is a welded connection, such
as where the shell 11 is welded to the surface 7 of the base.
The stack(s) 9 and the shell 11 can be removably connected using a
different type of connection from each other. Furthermore, in an
alternative aspect of the invention, the shell 11 may be removably
connected to the upper surface 7 of the base 3, while the stack(s)
9 may be non-removably connected to the same surface 7.
Preferably, at least one heat exchanger is located in the interior
volume 5 of the base 3. For example, as shown in FIG. 1B, a
multi-stream heat exchanger 13 is located in the interior volume 5
of the base 3.
The heat exchanger 13 may comprise a low temperature portion 15 and
a high temperature portion 17. The low temperature portion 15 may
be made of less expensive, low temperature materials, such as
stainless steel, which are not tolerant of very high temperatures.
The high temperature portion 17 may be made of more expensive, high
temperature materials, such as Inconel or other nickel alloys,
which are high temperature tolerant. This configuration decreases
the cost of the heat exchanger 13. If desired, one or more
intermediate temperature portions made of intermediate temperature
tolerant materials may also be provided in the heat exchanger
13.
Any type of heat exchanger may be used, such as a finned plate type
of heat exchanger. If desired, the high temperature portion 17 of
the heat exchanger may act as a complete or partial external
reformer 37 for the fuel cell stacks 9. In this case, the all or a
portion of fins of the passages of the heat exchanger 13 which
carry the fuel inlet stream are coated with a fuel reformation
catalyst, such as nickel and/or rhodium for a hydrocarbon fuel,
such as natural gas or methane. The external reformer 37 may act as
a pre-reformer if the stacks 9 contain fuel cells of the internal
reformation type (i.e., fuel cells contain one or more internal
surfaces or coatings that are catalytically active for reforming.
The catalyst may comprise a catalyst coating, or using nickel as
part of the metal construction of the fuel cell housing and
support). Alternatively, for complete internal reformation type
fuel cells or for fuel cell systems which operate on hydrogen fuel
(which does not require reformation), the reformer 37 may be
omitted. For external reformation type fuel cells (i.e., fuel cells
which do not contain a fuel reformation catalyst or fuel cells in
which the catalyst is part of the metal structure of the cell
housing, the catalyst may still be present, but not designed to be
used as a catalyst, usually due to degradation of the cells), the
reformer 37 acts as the main fuel reformer. In an alternative
embodiment of the invention, the reformer 37 is not integrated into
the heat exchanger but is located in a separate location in the hot
box of the module 1. In another alternative embodiment of the
invention, separate fuel and air heat exchangers provide heat from
the fuel and air exhaust streams, respectively, to fuel and air
inlet streams, respectively, as will be described with respect to
FIG. 2B below.
As shown in FIGS. 1A-1E, an anode tail gas oxidizer (ATO) 10 is
preferably located over the central portion of the base 3 (i.e., on
the base plate 7) in a heat transfer relationship with the stacks 9
(i.e., such that heat is transferred by convection and/or radiation
between the ATO 10 and the stacks 9). Preferably but not
necessarily, the ATO 10 is located in the middle of the annular
stack 9 array such that the ATO 10 is surrounded by the stacks 9.
However, for stack 9 layouts that do not form a complete ring, such
as grid or arc layouts, the ATO 10 may be located adjacent to the
stacks or may be partially surrounded by the stacks 9. In an
annular or arc array, the ATO is exposed to the radially inward
faces of the fuel cell stacks to receive the cathode exhaust stream
therefrom. An ATO is a chamber in which the anode (fuel) exhaust
from the stacks is oxidized by reaction with an oxidizer stream,
such as a reaction of the stack anode exhaust stream with the stack
cathode (air) exhaust stream. The ATO chamber walls may be coated
with a suitable oxidation reaction promoting catalyst, such as
palladium on a support member or material. The oxidation reaction
releases heat which can be used to heat the stacks 9 and/or to
provide a hot ATO exhaust stream into the heat exchanger 13. As
shown in FIG. 1B, the ATO 10 may comprise an ATO exterior baffle
12, which is a cylindrical or other suitably shaped wall which is
attached to the top of the outer shell 11, but which contains an
opening 18 adjacent to the base plate 7 of the base 3 through which
the stack cathode (air) exhaust stream passes. The ATO 10 may also
comprise an interior baffle 14 which is a cylindrical or other
suitably shaped wall which is attached to the base plate 7 but
which contains an opening 20 adjacent to the upper surface of the
shell 11 through which the anode and cathode exhaust streams pass.
The interior baffle 14 is preferably located inside the exterior
baffle 12. The interior baffle 14 may also be considered as an
annulus for the ATO/cathode exhaust conduit 27. The interior and/or
exterior surface of the interior baffle 14 and/or the interior
surface of the exterior baffle 12 may be covered with the oxidation
promoting catalyst material, which may be coated on optional fins
or corrugations 16 located on the surface(s) of the baffle(s) 12,
14. For example, while FIG. 1B shows a two pass ATO (up flow, then
down flow), the ATO 10 may have more passes, and the interior
baffle 14 may contain perforations. Alternatively, the interior
baffle 14 may extend to the top of the shell 11 and only have
perforations rather than the opening 20 near the top.]
One or more ATO fuel inlet conduit(s) 22 are located in the base
plate 7 between the exterior 12 and the interior 14 ATO baffles.
The ATO fuel inlet conduits 22 provide the ATO fuel inlet stream
between the baffles 12 and 14 where the fuel inlet stream mixes and
reacts with the ATO air inlet stream. The ATO fuel inlet stream may
comprise one or both of i) a separate fuel inlet stream from the
stack fuel inlet stream, such as a natural gas inlet stream, and/or
ii) at least a portion of the stack anode exhaust stream that has
passed through the heat exchanger 13. Alternatively, the ATO fuel
inlet stream may also partially or fully bypass the heat exchanger
to keep the inlet temperature limited. The ATO air inlet stream may
comprise the stack cathode exhaust stream which flows from the
stacks 9 to the ATO 10 under the outer baffle 12, as shown in FIG.
1B, or a fresh air inlet stream (which may or may not be mixed with
either of the ATO fuel inlet streams), or a combination of fresh
air inlet stream and stack cathode exhaust. The ATO fuel inlet
stream is oxidized by the ATO air inlet stream (such as the stack
cathode exhaust stream or a mixture of the cathode exhaust and the
optional fresh air inlet streams]. The ATO exhaust stream (oxidized
fuel) is removed from the ATO 10 through the central ATO exhaust
conduit 27 located in the base plate 7 in the middle of the
interior baffle 14.
As shown in FIGS. 1B and 1C, the base 3 also contains a plurality
of fuel inlets 21 which provide a fuel inlet stream to the fuel
cell stacks 9, a plurality of fuel exhaust openings 23 which remove
the fuel exhaust stream from the stacks 9, a plurality of
peripheral air inlets 25 which provide an air (or other oxidizer)
inlet stream to the stacks 9, and a central ATO exhaust conduit 27
which removes the air/ATO exhaust stream from the stacks 9. Inlets
21 and 25 and exhaust opening 23 may comprise holes in the base
plate 7 and/or pipes which extend through the base plate 7. Thus,
in one embodiment of the invention, the stacks 9 are externally
manifolded for air and internally manifolded for fuel. The
plurality of angularly spaced fuel cell stacks 9 are arranged to
form an annular array about a central axis of the module inside the
ring-shaped arrangement of the stack air inlets 25.
The module 1 operates as follows. The fuel and air inlet streams
are heated in the heat exchanger 13 by the anode exhaust and/or the
ATO exhaust streams, as will be described in more detail below. The
fuel inlet stream is provided upwards and internally into the
stacks 9 through the respective fuel inlets 21 for each stack from
below. The anode (fuel) exhaust stream from the stacks 9 is
provided downwards and internally through the stacks and is removed
through the respective fuel exhaust openings 23 into the heat
exchanger 13 located in the base 3.
As shown by the arrows in FIG. 1B, the stack air inlet stream is
provided under the shell 11 through the base plate 7 through inlets
25 arranged in an annular or ring shaped configuration in the
periphery of the base 3. The air inlet stream flows through the
cells of the stacks 9. The stacks 9 and ceramic spacers (which are
not shown for clarity) prevent the air inlet stream from flowing
directly into the interior space 24 without flowing though the
stacks 9 first. The cathode (air) exhaust stream exits the stacks 9
into the space 24 between the stacks 9 and the outer ATO baffle 12.
The cathode exhaust stream flows through opening(s) 18 below the
outer ATO baffle 12 into the space 26 between the outer and inner
ATO baffles 12, 14. The stack cathode exhaust stream mixes and
reacts with the ATO fuel inlet stream provided from conduits 20 in
space 26. The oxidation reaction provides heat to the stacks 9 via
radiation and/or convection during system start-up and during
steady state operation to provide sufficient heat for internal fuel
reformation reaction in the stacks 9. The ATO exhaust (oxidized
fuel) is then exhausted upwards through opening(s) 20 above the
inner baffle 14 and downward through the central ATO exhaust
conduit 27 into the heat exchanger 13 located in the chamber 5
below the base plate 7. While a specific ATO configuration is shown
in FIGS. 1B and 1C, it should be understood that other
configurations may also be used, such as configurations where the
fluid streams follow a linear or tortuous path adjacent to
oxidation catalyst coated members. For example, a cylinder may be
located inside baffle 14 to limit the volume (and hence the amount)
of fins and catalyst.
As shown in FIGS. 1A-1C, a fuel inlet line 29 is connected to a
first inlet of the fuel heat exchanger 13. The plurality of fuel
inlet conduits 21 are fluidly connected to a first outlet of the
heat exchanger 13. The term "fluidly connected" means either
directly connected or indirectly connected such that the fuel inlet
stream flows from the heat exchanger 13 through one or more other
components until it reaches each fuel inlet conduit 21. The
plurality of fuel exhaust openings 23 are fluidly connected to a
second inlet of the heat exchanger 13. A fuel exhaust line 31 is
connected to a second outlet of the heat exchanger 13. An air inlet
line 33 is connected to a third inlet of the heat exchanger 13. If
desired, one or more optional air by-pass conduits may be provided
which diverts some or all of the air inlet stream from the air
inlet line 33 around the heat exchanger 13, or around a portion of
the heat exchanger 13. Thus, the by-pass conduit(s) may connect the
air inlet line 33 directly to the stack 9 air inlet. The amount of
air provided into the by-pass conduit(s) can be controlled by flow
regulator, such as a computer or operator controlled valve. The
plurality of air inlet conduits 25 in the base are fluidly
connected to a third outlet of the heat exchanger 13. The central
air/ATO exhaust conduit 27 is fluidly connected to a fourth inlet
of the heat exchanger 13. An air/ATO exhaust line 35 is connected
to a fourth outlet of the heat exchanger 13. If desired, the heat
exchanger 13 may have separate air and ATO exhaust lines (i.e.,
some or all of the hot air exhaust may bypass the ATO, which can
instead use fresh inlet air for the oxidation reaction).
Preferably, the base 3 and the shell 11 are also used to provide an
electrical connection from the stacks 9 to the power conditioning
equipment. For example, the upper surface 7 of the base 3 may
contain a plurality of electrical contacts 41 such as negative or
ground electrical contacts. Each contact 41 is located where a
bottom end plate of a fuel cell stack 9 would touch the base plate
7 (i.e., the upper surface) of the base 3. Each negative or ground
electrode or end plate of each fuel cell stack 9 is electrically
connected to one of the plurality of electrical contacts 41. The
base 3 also contains a common electrical bus 43, such as a negative
or ground bus, which is electrically connected to the fuel cells 9
through the contacts 41.
The shell 11 contains at least one other electrical bus 45, such as
a separate electrical bus 45 for each stack 9. The bus 45 has a
different polarity than the polarity of the common electrical bus
43. For example, the shell 11 may have a plurality of positive
buses 45. A positive electrode or end plate of a fuel cell stack 9
is electrically connected to a respective positive electrical bus
45 extending from the shell 11.
The positive electrode or end plate of each fuel cell stack 9 may
be electrically connected to the respective positive electrical bus
45 using any suitable contact or electrical connection. For
example, as shown in FIG. 1B, an upper interior surface of the
shell 11 contains a plurality of electrically conductive pressure
members 47. The pressure members 47 on the shell 11 are aligned
with the stack 9 positions over the contacts 41 on the upper
surface 7 of the base 3. Each pressure member 47 removably holds at
least one fuel cell stack 9 between the shell 11 and the upper
surface 7 of the base 3. The positive electrode or end plate of
each fuel cell stack 9 is electrically connected to the positive
electrical bus 45 through a respective pressure member 47. The
pressure member 47 may be a flexible bar, plate or spring which
puts a downward pressure on the stack 9 to keep the stack 9 firmly
against the electrical contact 41 on the upper surface 7 of the
base. When the shell 11 is pushed down to close the module 1, the
pressure member flexes to press the stack 9 into place on the base
3. When the shell 11 is removed to service or repair the module,
the pressure member releases the stack 9.
Preferably, but not necessarily, each stack 9 or each pair of
stacks 9 are connected to a separate DC/DC converter unit of the
power conditioning system. For example, one electrical input/output
of each stack in each pair of stacks may be connected in series and
the other electrical input/output of each stack in each pair of
stacks provides a respective positive and negative voltage inputs
into the respective DC/DC converter unit. Preferably, but not
necessarily, the fuel cell stacks (i.e., fuel cell stack columns)
may be arranged in a multiple of six to simplify power
conditioning, as described in U.S. application Ser. Nos. 11/797,707
and 11/707,708, filed on May 5, 2007 and incorporated herein by
reference in their entirety. Thus, each module may have 6, 12, 18,
24, etc. stacks 9. For example, the module 1 shown in FIGS. 1C to
1E contains twelve stacks 9. Each set of four stacks may be
connected to one respective phase output of a three phase AC
output, as described in U.S. application Ser. No. 11/797,707.
Thus, in a system comprising a plurality of modules, each module 1
may be electrically disconnected, removed from the fuel cell system
and/or serviced or repaired without stopping an operation of the
other modules 1 in the fuel cell system. In other words, each
module 1 may be electrically disconnected, removed from the fuel
cell system and/or serviced or repaired while the other modules 1
continue to operate to generate electricity. Thus, the entire fuel
cell system does not have to be shut down when one stack 9
malfunctions or is taken off line for servicing.
When one module 1 is taken off line (i.e., it is turned off to be
removed, repaired or serviced), while the other modules 1 continue
to operate, the flow of fuel to the module 1 which is taken off
line should be stopped. This may be accomplished by placing valve
in each fuel inlet line 29. The valve may be turned off manually or
electronically to stop the flow of fuel through a given fuel inlet
line 29, while the fuel continues to flow through the other fuel
inlet lines 29 to the other modules 1.
The second embodiment of the invention provides a multi-stream heat
exchanger 13 for a fuel cell system, where more than two fluid
streams exchange heat in the same device. Thus, a single
multi-stream heat exchanger can replace multiple separate heat
exchangers, such as separate air and fuel heat exchangers, used in
prior art systems. The multi-stream heat exchanger allows for the
same amount of heat exchange as separate fuel and air heat
exchangers, but with a smaller amount of heat transfer area due to
more uniform temperature differences between the hot streams and
cold streams. Furthermore, if desired, a steam generator and/or an
external reformer 37 may be physically integrated into the
multi-stream heat exchanger 13 such that the heat of the fuel cell
stack 9 anode exhaust stream and/or ATO 10 exhaust stream is used
to convert water to steam and/or to provide heat for a hydrocarbon
fuel to hydrogen and carbon monoxide fuel reformation reaction,
such as a steam-methane reformation ("SMR") reaction.
The multi-stream heat exchanger 13 may serve as a base or be
located in the base 3 for building the hot box of the fuel cell
system. Thus, the multi-stream heat exchanger 13 lowers the center
of gravity of the module 1 and makes the module more stable. The
use of a single multi-stream heat exchanger 13 reduces the number
of air flow controls in the system from two to one. The ATO air
flow control may be eliminated. It makes the system integration
simpler by reducing the amount of additional plumbing. Furthermore,
the multi-stream heat exchanger 13 increases the efficiency of the
system, facilitating better heat transfer, removing pinch points
and reducing the parasitic losses, including the gain from the
elimination of the ATO air blower. Finally, the multi-stream heat
exchanger 13 allows the use of a combination of low and high
temperature materials in zones 15 and 17 to reduce the cost of the
device.
FIG. 2A illustrates a process flow diagram for a fuel cell system
100 containing one or more modules 1 of the second embodiment. One
module 1 is shown for clarity in FIG. 2A. The system 100 contains
the plurality of the fuel cell stacks 9, such as a solid oxide fuel
cell stacks (where one solid oxide fuel cell of the stack contains
a ceramic electrolyte, such as yttria stabilized zirconia (YSZ) or
scandia stabilized zirconia (SSZ), an anode electrode, such as a
nickel-YSZ or Ni-SSZ cermet, and a cathode electrode, such as
lanthanum strontium manganite (LSM)). The module 1 is represented
as a hot box which may comprise the combination of the base 3 and
the shell 11, as shown in FIG. 1B. The optional reformer 37 is
shown separately from the heat exchanger 13. However, as noted
above, the heat exchanger 37 may be physically integrated into the
heat exchanger 13.
The system 100 also contains a steam generator 103. The steam
generator 103 is provided with water through conduit 30A from a
water source 104, such as a water tank or a water pipe, and
converts the water to steam. The steam is provided from generator
103 to mixer 105 through conduit 30B and is mixed with the stack
anode (fuel) recycle stream in the mixer 105. The mixer 105 may be
located inside or outside the hot box of the module 1. Preferably,
the humidified anode exhaust stream is combined with the fuel inlet
stream in the fuel inlet line or conduit 29 downstream of the mixer
105, as schematically shown in FIG. 2A. Alternatively, if desired,
the fuel inlet stream may also be provided directly into the mixer
105, or the steam may be provided directly into the fuel inlet
stream and/or the anode exhaust stream may be provided directly
into the fuel inlet stream followed by humidification of the
combined fuel streams, as shown in FIGS. 1C, 1D and 1E.
The steam generator 103 may be heated by a separate heater and/or
by the hot ATO exhaust stream which is passed in heat exchange
relationship with the steam generator 103. If the steam generator
103 is physically incorporated into the heat exchanger 13, then the
steam generator may also be heated by the anode exhaust stream in
the heat exchanger. The steam generator 103 may be physically
located in the hot box, such as inside the chamber 5 of the base 3.
Alternatively, the steam generator 103 may be located outside the
hot box of the module 1. Thus, as shown in FIG. 1C, if the steam
generator 103 is located in the hot box of the module, then water
is provided from the water source 104 through conduit 30. If the
steam generator 103 is located outside of the hot box of the
module, then steam is provided from the water source 104 through
conduit 30.
The system 100 also contains a splitter 107, an optional water trap
109 and a catalytic partial pressure oxidation (CPOx) reactor 111.
The water trap 109 and drain are not required if the anode exhaust
stream provided to the ATO 10 can be kept sufficiently hot to avoid
condensation. The system operates as follows. The inlet fuel
stream, such as a hydrocarbon stream, for example natural gas, is
provided into the fuel inlet conduit 29 and through the CPOx
reactor 111. During system start up, air is also provided into the
CPOx reactor 111 to catalytically partially oxidize the fuel inlet
stream. During steady state system operation, the air flow is
turned off and the CPOx reactor acts as a fuel passage way in which
the fuel is not partially oxidized. Thus, the system 100 may
comprise only one fuel inlet conduit which provides fuel in both
start-up and steady state modes through the CPOx reactor 111.
Therefore a separate fuel inlet conduit which bypasses the CPOx
reactor during steady state operation is not required.
The fuel inlet stream is provided into the multi-stream heat
exchanger 13 where its temperature is raised by heat exchange with
the ATO exhaust stream and the stack anode (fuel) exhaust streams.
The fuel inlet stream is then optionally provided into the optional
reformer 37 which may be integrated into the heat exchanger 13 or
be located in the hot box separately from the heat exchanger 13.
The fuel inlet stream is reformed in the reformer via the SMR
reaction and the reformed fuel inlet stream (which includes
hydrogen, carbon monoxide, water vapor and unreformed methane) is
provided into the stacks 9 through the fuel inlets 21. The fuel
inlet stream travels upwards through the stacks through fuel inlet
risers in the stacks 9 and is oxidized in the stacks 9 during
electricity generation. The oxidized fuel (i.e., the anode or fuel
exhaust stream) travels down the stacks 9 through the fuel exhaust
risers and is then exhausted from the stacks through the fuel
exhaust opening 23 into the heat exchanger 13.
In the heat exchanger 13, the anode exhaust stream heats the fuel
inlet stream and the air inlet stream via heat exchange. The anode
exhaust stream is then provided via the fuel exhaust conduit 31
into a splitter 107. A first portion of the anode exhaust stream is
provided from the splitter 107 into the water trap 109. In the
water trap 109, the water is removed from the anode exhaust stream
and the removed water is stored or drained via drain 112. The
remaining anode exhaust stream may be provided from the water trap
109 into the ATO 10 via conduit 113. The anode exhaust stream may
be provided with fresh fuel, such as natural gas from conduit 115
into the ATO 10 through fuel inlets 22 as a combined ATO fuel inlet
stream.
A second portion of the anode exhaust stream is recycled from the
splitter 107 into the fuel inlet stream. For example, the second
portion of the anode exhaust stream is recycled through conduit 117
by a blower (not shown in FIG. 2A) into the mixer 105. The anode
exhaust stream is humidified in the mixer 105 by mixing with the
steam provided from the steam generator 103. The humidified anode
exhaust stream is then provided from the mixer 105 into the fuel
inlet conduit 29 where it mixes with the fuel inlet stream.
Providing water from the water tank 104 to make steam is optional.
All of the humidification for the fresh fuel can be provided by
anode recycle stream.
The air inlet stream is provided by a blower (not shown) from the
air inlet conduit 33 into the heat exchanger 13. The blower may
comprise the single air flow controller for the entire system. In
the heat exchanger, the air inlet stream is heated by the ATO
exhaust stream and the anode exhaust stream via heat exchange. The
heated air inlet stream is then provided into the module through
the air inlets 25. The air passes through the stacks 9 into the ATO
10. In the ATO 10, the air exhaust stream oxidizes the ATO fuel
inlet stream to generate an ATO exhaust stream. The ATO exhaust
stream is exhausted through the ATO exhaust conduit 27 into the
heat exchanger 13. The ATO exhaust stream heats the fuel and air
inlet streams in the heat exchanger 13 via heat exchange. The ATO
exhaust stream (which is still above room temperature) is provided
from the heat exchanger 13 to the steam generator 103 via conduit
119. The heat from the ATO exhaust stream is used to convert the
water into steam via heat exchange in the steam generator 103. The
ATO exhaust stream is then removed from the system via conduit 35.
If the steam generator 103 is physically integrated into the heat
exchanger 13, then conduit 119 can be omitted and the steam
generation takes place in the heat exchanger 13. Thus, by
controlling the air inlet blower output (i.e., power or speed), the
magnitude (i.e., volume, pressure, speed, etc.) of air introduced
into the system may be controlled. The cathode (air) exhaust stream
is used as the ATO air inlet stream, thus eliminating the need for
a separate ATO air inlet controller or blower. Furthermore, since
the ATO exhaust stream is used to heat the air and fuel inlet
streams, the control of the single air inlet stream in conduit 33
can be used to control the temperature of the stacks 9 and the ATO
10. If the air by-pass conduit is present, then this conduit
enhances the ability to control the stack 9 and ATO 10 temperature
by controlling the amount of air provided into the heat exchanger
13 compared to the amount of air provided directly into the stacks
9 through the by-pass conduit.
FIGS. 3 and 4 illustrate the fluid flows though an exemplary five
zone heat exchanger 13. The zones are labeled Z1 to Z5 in FIG. 4.
It should be noted that the heat exchanger 13 may have less than
five zones, such as one to four zones or more than five zones, such
as six to ten zones. The heat exchanger may be a counterflow, a
co-flow or a combination thereof heat exchanger type having a plate
and fin or other suitable configuration. Furthermore, the order of
fluid flow introduction and the flow stream temperatures described
below are exemplary and may be changed depending on the specific
system configuration.
The cold air inlet stream enters zone 1 of the heat exchanger at
about room temperature from conduit 33 and is heated by the hot
anode exhaust stream. The anode exhaust stream gives up some of its
heat and exits as warm anode exhaust stream (at a temperature of
about 100 C, for example) into conduit 31.
The warmed air inlet stream (at a temperature of about 100 C) is
provided from zone 1 into zone 2 of the heat exchanger. The
relatively cold fuel inlet stream (which has been warmed to about
100 C by the addition of the steam from the steam generator and of
the recycled anode exhaust stream from conduit 117) is also
provided from conduit 29 into zone 2 of the heat exchanger. The air
and fuel inlet streams are not mixed but flow through different
respective channels in zone 2 separated by the heat exchanger
plates, or in separate channels of a single heat exchanger plate.
The air and fuel inlet streams are heated by the hot anode exhaust
stream in zone 2 via heat exchange across the heat exchanger
plates.
The warmed air and fuel inlet streams (at a temperature of about
150 C) are provided into zone 3 of the heat exchanger 13. The hot
anode exhaust stream also first enters the heat exchanger 13 in
zone 3 at a temperature of about 800 C. The air and fuel inlet
streams are heated by the hot anode exhaust stream and by the hot
ATO exhaust stream in zone 3 via heat exchange across the heat
exchanger plates. The anode and ATO exhaust streams are not mixed
but flow through different respective channels in zone 3 separated
by the heat exchanger plates. After exchanging heat, the warm ATO
exhaust stream exits the heat exchanger 13 in zone 3 into conduit
119 at a temperature of about 300 C. The ATO exhaust stream is then
used to generate steam in the steam generator 103. As can be seen
from FIGS. 3 and 4, zone 3 may be the largest or longest zone of
the heat exchanger 3 (i.e., the zone with the longest fluid flow
channel length) where the fluid streams spend the longest time of
any zone in the heat exchanger.
The further warmed air and fuel inlet streams (at a temperature of
about 600 C) are provided into zone 4 of the heat exchanger 13. The
air and fuel inlet streams are heated by the hot ATO exhaust stream
in zone 4 via heat exchange across the heat exchanger plates. The
warmed up air inlet stream exits the heat exchanger 13 in zone 4
into conduits 25 at a temperature of about 650 C to be provided
into the fuel cell stacks 9.
The further warmed fuel inlet stream (at a temperature of about 650
C) is provided into zone 5 of the heat exchanger 13. The ATO
exhaust stream first enters the heat exchanger 13 in zone 5 from
conduit 27 at a temperature of about 875 C. The fuel inlet stream
is heated by the hot ATO exhaust stream in zone 5 via heat exchange
across the heat exchanger plates. The warmed up fuel inlet stream
exits the heat exchanger 13 in zone 5 into conduits 21 at a
temperature of about 750 C to be provided into the fuel cell stacks
9 (and/or into the reformer 37 if a separate reformer is
present).
As shown in FIG. 3, a gap due to an about 1% heat exchanger leak is
assumed. Furthermore, as shown in FIG. 3, the hot streams (ATO and
anode exhaust streams) are maintained at about the same temperature
as each other in each zone where they are both present. Likewise,
the cold streams (air and fuel inlet streams) are maintained at
about the same temperature as each other in each zone where they
are both present. Finally, the global pinch point is shown in FIG.
3 if the heat exchanger 13 is designed based on pinch
technology.
With respect to FIG. 1B, the low temperature portion 15 of the heat
exchanger 13 may correspond to zones 1 and 2 (and optionally an
adjacent portion of zone 3) shown in FIG. 4, while the high
temperature portion 17 of the heat exchanger 13 may correspond to
zones 4 and 5 (and optionally an adjacent portion of zone 3) shown
in FIG. 4.
FIG. 2B illustrates a schematic of a system 200 according to
another embodiment of the invention in which the single
multi-stream heat exchanger 13 is replaced with separate heat
exchangers. The commonly numbered elements which are common to both
system 100 of FIG. 2A and system 200 of FIG. 2B will not be
described again for the sake of brevity. As shown in FIG. 2B, the
multi-stream heat exchanger 13 is replaced with a fuel heat
exchanger 137, an air heat exchanger 203 and an optional air
preheater heat exchanger 205.
As shown in FIG. 2B, the external reformer 37 may be omitted if the
fuel cells or the fuel cell stack 9 contain internal fuel
reformation catalyst. Alternatively, the fuel heat exchanger 137
may contain the reformation catalyst in the fuel inlet portion of
the heat exchanger. In this case, the heat exchanger 137 functions
as both a heat exchanger and a reformer.
If desired, the water trap 109 may be omitted and the entire
portion of fuel exhaust stream provided from splitter 107 into
conduit 113 may be recycled into the ATO 113.
Furthermore, the natural gas inlet conduit 115 into the ATO 10 may
be omitted. Instead all of the fuel for the ATO 10 may be provided
from the fuel cell stack 9 anode tail gas recycle conduit 113. For
a thermally well packaged system with internal fuel reformation,
the introduction of fresh fuel into the ATO 10 through conduit 115
may be omitted. Instead, the amount of fresh fuel provided to the
stack 9 via conduit 29 is controlled or adjusted to control the
heating up process. The elimination of the separate fuel conduit to
the ATO (and associated fuel blower) and the use of the stack
cathode exhaust stream as the source of oxidizer gas in the ATO 10
(instead of using a separate air inlet conduit to provide fresh air
into the ATO 10) reduces the complexity and cost of the fuel cell
and control systems and method of operating the system. For
example, control of the main air inlet stream in conduit 33 may be
used as the main control for the system temperature.
The system 200 shown in FIG. 2B operates similarly to the system
100 shown in FIG. 2A. However, in the system 200, the air inlet
stream in conduit 33 is first provided into the optional air
preheater heat exchanger 205 where the air inlet stream is
preheated by the fuel (anode) exhaust stream. The terms fuel
exhaust and anode exhaust are used interchangeably herein with
respect to solid oxide fuel cell stacks. The preheated air inlet
stream is then provided into the air heat exchanger 203 where it is
heated by the ATO 10 exhaust stream from conduit 27. The ATO
exhaust stream is then provided from the air heat exchanger 203 via
conduit 119 to the steam generator 103. The hydrocarbon fuel inlet
stream is provided via the fuel inlet conduit 29 into the fuel heat
exchanger 137. The fuel inlet stream is then provided into the fuel
cell stack(s) 9 via conduit 21 where the fuel inlet stream may be
reformed internally. Alternatively, a separate external reformer 37
or an external reformer integrated into heat exchanger 137 may be
used instead. The fuel exhaust stream is provided form the stack(s)
9 into the fuel heat exchanger 137 via conduit 23A. The fuel
exhaust stream is then provided from the fuel heat exchanger 137
via conduit 23B into the optional air preheater heat exchanger 205.
The fuel exhaust stream is then provided from the air preheater
heat exchanger 205 via conduit 31 into the splitter 107.
If desired, the reformer 37 and/or the steam generator 103 may
optionally be integrated into the existing zones of the heat
exchanger or they may be added as additional zones. For example,
the reformer catalyst may be provided into the fuel inlet stream
conduits in zones 3, 4 and/or 5 to integrate the reformer 37 into
the heat exchanger 13.
The steam generator 103 may be physically integrated with the heat
exchanger by adding the steam generator as one or more extra zones
to the heat exchanger 13. FIG. 5 illustrates a process flow diagram
for a system 200 containing a steam generator which is integrated
into multi-stream heat exchanger 13/103. In the example of FIG. 5,
the heat exchanger contains seven zones. However, a heat exchanger
containing more than or less than seven zones may be used. Other
elements shown in FIG. 5 having the same numbers as elements in
FIG. 2A have been described above with respect to FIG. 2A and will
not be described again with respect to FIG. 5 for brevity. The
exemplary temperatures in each element are shown in a circle above
the element. It should be noted that other suitable temperatures
may be used.
The following table describes the hot and cold fluid flow streams
passing through each of the seven zones Z1 to Z7 of the integrated
heat exchanger/steam generator 13/103:
TABLE-US-00001 Zone Cold Side Stream Hot Side Stream Z1 Water ANEXH
Z2 Water, Air ANEXH Z3 Water, Air ANEXH, ATO-EXH Z4 Water, Air,
Fuel-mix ANEXH, ATO-EXH Z5 Air, Fuel-mix ANEXH, ATO-EXH Z6 Fuel-mix
ANEXH, ATO-EXH Z7 Fuel-mix ATO-EXH
In the table above, "water" corresponds to the water inlet stream
from the water source 104 and conduit 30A, "air" corresponds to the
air inlet stream from conduit 33, "fuel-mix" corresponds to the
humidified fuel inlet stream from conduit 29, "ANEXH" corresponds
to the anode exhaust stream from conduit 23 and ATO-EXH corresponds
to the ATO exhaust stream from conduit 27. Thus, "water" is present
in zones Z1 to Z4 (enters in Z1 and exits in Z4), "air" is present
in zones Z2 to Z5 (enters in Z2 and exits in Z5) and "fuel-mix" is
present in zones Z4 to Z7 (enters in Z4 and exits in Z7). These
cold side streams are heated by the "ANEXH" stream in zones Z1 to
Z6 (enters in Z6 and exits in Z1) and by the ATO-EXH stream in
zones Z3 to Z7 (enters in Z7 and exits in Z3).
Thus, zone Z1 corresponds to the steam generator 103, zones Z2 to
Z4 correspond to a hybrid steam generator/heat exchanger, and zones
Z5 to Z7 corresponds to the heat exchanger. Of course other heat
exchanger and flow configurations may also be used. It should be
noted that in FIG. 5, if a liquid hydrocarbon fuel is used, then
the liquid fuel may be provided into the steam generator together
with the water to vaporize the liquid fuel. An optional liquid
fuel/water mixer 201 may be used to mix the liquid fuel and water.
Furthermore, an optional ATO fuel/anode exhaust mixer 203 may be
used to mix the ATO fuel, such as natural gas in conduit 115, with
the anode exhaust in conduit 113, prior to providing the mixed fuel
into the ATO inlet 22.
FIGS. 6 and 7 are non-limiting, three dimensional cut-away views of
two types of multi-stream plate heat exchangers. In should be noted
that other heat exchanger configurations may be used. FIG. 6 shows
a heat exchanger 300 configuration where two streams exchange heat
in each zone (such as zones Z1 and Z5 shown in FIG. 4). For
example, streams 301 and 302 exchange heat in zone 304 and stream
301 and 302 exchange heat in zone 305. Each zone 304, 305 contains
ribbed or finned heat exchange plates 306. An inlet/outlet manifold
307 is located between the zones.
FIG. 7 shows another heat exchanger 310 configuration where two
cold streams R1 and R2 (such as the air and fuel inlet streams)
exchange heat with a hot water containing stream, such as the anode
or ATO exhaust stream (which corresponds to zones Z2 and Z4 shown
in FIG. 4). These configurations can be easily extended to four
fluid streams (such as zone 3 shown in FIG. 4). The heat exchanger
310 may be similar to the plate type heat exchanger 300 and contain
heat exchanger plates 316. However, for example, each plate 316 may
contain six openings 317 to accommodate three inlets and three
outlets of the three streams and the three streams are provided in
every third space between the parallel plates 316. The heat
exchanger may be configured to handle more than three streams and
may have different configurations other than parallel plate type
configurations.
Another embodiment of the invention provides a modular design for
the entire fuel cell system rather than just for the fuel cell
stack modules. The modular system design provides flexible
installation and operation. Modules allow scaling of installed
generating capacity, reliable generation of power, flexibility of
fuel processing, and flexibility of power output voltages and
frequencies with a single design set. The modular design results in
an "always on" unit with very high availability and reliability.
This design also provides an easy means of scale up and meets
specific requirements of customer's installations. The modular
design also allows the use of available fuels and required voltages
and frequencies which may vary by customer and/or by geographic
region. Thus, in summary, since the fuel cell system is designed as
a modular set, it can be installed to accommodate the requirements
of different customers and the elements of the system are able to
work in concert to achieve a very high system reliability and
availability.
FIG. 8 shows an exemplary configuration of the modular fuel cell
system 60. The system 60 includes the following elements. The
system 60 includes a plurality of fuel cell stack modules 61. These
modules 61 are devices which contain the components used for
generating DC power from a readily reformed fuel stream.
In one aspect of the second embodiment, each fuel cell stack module
61 is the same as the module 1 of the first embodiment. Thus, each
module 61 shown in FIG. 8 may comprise a base 3, a shell 11 and one
or more fuel cell stacks 9, as shown in FIG. 1B. For example, for a
high temperature fuel cell system, such as a SOFC or a molten
carbonate fuel cell system, each fuel cell stack module 61 is the
same as the module 1 of the first embodiment. In an alternative
aspect of the second embodiment, each module 61 may comprise one
base 3 and a plurality of fuel cell stacks 9 covered by a plurality
of shells 11. Alternatively, each module 61 may have a different
structure or configuration from the modules 1 of the first
embodiment. For example, for low temperature fuel cell systems,
such as PEM systems, each module 61 can be different from the
module 1 of the first embodiment. Thus, the system of the second
embodiment is applicable to high and low temperature fuel cell
stack modules.
Each module 61 contains at least one fuel cell stack 9. Multiple
fuel cell stack modules 61 may be installed in a clustered
installation, such as for example, in a single hot box 62. A
failure of a single fuel cell stack module 61 results only in a
slightly degraded output capacity or slightly degraded system
efficiency because the remaining fuel cell stack modules 61
continue operation.
The system 60 also contains one or more fuel processing modules 63.
These modules are devices which contain the components used for
pre-processing of fuel so that it can be readily reformed. The fuel
processing modules 61 may be designed to process different sets of
fuels. For example, a diesel fuel processing module, a natural gas
fuel processing module, and an ethanol fuel processing module may
be provided. The processing modules 63 may processes at least one
of the following fuels selected from natural gas from a pipeline,
compressed natural gas, propane, liquid petroleum gas, gasoline,
diesel, home heating oil, kerosene, JP-5, JP-8, aviation fuel,
hydrogen, ammonia, ethanol, methanol, syn-gas, bio-gas, bio-diesel
and other suitable hydrocarbon or hydrogen containing fuels. If
desired, the reformer 37 may be located in the fuel processing
module 63. Alternatively, if it is desirable to thermally integrate
the reformer 37 with the fuel cell stack(s) 9, then the reformer(s)
37 may be located in the fuel cell stack module(s) 61. Furthermore,
if internally reforming fuel cells are used, then the external
reformer 37 may be omitted entirely.
The system 60 also contains one or more power conditioning modules
65. These modules 65 are devices which contain the components for
converting the DC power to AC power, connecting to the grid, and
managing transients. The power conditioning modules 65 may be
designed convert the DC power from the fuel cell modules 61 to
different AC voltages and frequencies. Designs for 208V, 60 Hz;
480V, 60 Hz; 415V, 50 Hz and other common voltages and frequencies
may be provided. For example, each module 65 may contain a
dedicated DC/DC converter unit for each pair of stacks 9 in a fuel
cell module 61 and a common DC/AC converter unit for the plural
DC/DC converter units of each module 65.
Each type of module 61, 63, 65 may be installed in or on a separate
container, such as a box, rack or platform. Thus, the containers
may be located separately from each other, and may be moved,
repaired or serviced separately. For example, as shown in FIG. 8,
the fuel cell stack modules 61 are located in a common hot box 62.
The fuel processing module or modules 63 may be located in a
separate box 67. The power conditioning module or modules 65 may be
located on a separate rack 69.
Manifold Base Assembly.
In another embodiment of the invention, the base 3 shown in FIGS.
1A-1E is formed as a cast metal part. For example, the base 3 is
formed by casting a metal into a mold. Metal casting greatly
reduces the cost of manufacturing this component. Metal casting is
a well known manufacturing process which could easily achieve the
desired features and detail.
In another embodiment, the base 3 is fabricated as a single
manifold. The manifold may be formed by metal casting and/or by any
other suitable methods. This manifold contains hardware for rapid
connection and removal of all external plumbing at a single point
of connection for servicing ease. This manifold also contains
direct connections for any auxiliary reactors such as the CPOx
reactor 111 and/or the ATO 10. The manifold also contains the
plumbing (i.e., pipes and other conduits, such as conduits 31 and
117) used for anode exhaust stream recirculation. By making all
plumbing internal to the manifold, the materials cost of plumbing
and insulation is reduced. By making the manifold a single cast
piece, the assembly and repair time for a hot box is significantly
reduced.
As shown in FIG. 9, in this embodiment, the auxiliary reactors,
such as the ATO 10 and CPOx 111 may be formed on the surface 7 of
the base 3 or in the inner chamber 5 of the base 3 outside or below
the boundaries of the hot box (i.e., shell) 11, respectively.
Alternatively, one auxiliary reactor may be formed on the surface 7
of the base 3 while the other auxiliary reactor is formed in the
inner chamber 5 of the base. The conduits, such as conduits 24, 27,
29, 31, 113, 117, etc., that connect the auxiliary reactors to the
fuel cell stacks 9 inside the shell (i.e., hot box) 11 are located
in the inner chamber 5 and/or in the surface 7 of the base 3.
Likewise, the steam generator 103 and mixer 105 may be located
inside the shell 11, in the inner chamber 5 of the base 3, on the
surface 7 of the base 3 or in another location.
Single Shell Hot Box.
In another embodiment shown in FIG. 10, the air inlet 25 and
outlets 27 are reversed compared to FIG. 9. In the configuration of
FIG. 10, the air inlet stream flows into a central plenum or
manifold 25 from above or below. The air inlet stream then flows
radially though the stacks 9. The cathode (air) exhaust stream then
exits the stacks 9 in the peripheral portion of the module 1
through the air outlet openings 27 in the surface 7 of the base
3.
In this embodiment, an air heat exchanger 125 may be incorporated
into the shell 11 as shown in FIG. 11. The heat exchanger 125
comprises a separator wall 127 which separates an air inlet conduit
33 from the air exhaust conduit 27. The wall 127 may contain fins,
ridges or grooves 129 on one or both surfaces that facilitate heat
transfer between the air streams. In operation, the air inlet
stream enters from the base 3 through the air inlet conduit 33
which is located between the upper/outer side of wall 127 and the
bottom/inner surface of the shell 11. The air inlet stream is then
provided from conduit 33 into the central plenum 25 from which it
flows radially outward into the stacks 9. The cathode (air) exhaust
stream flows from the stacks 9 into the air exhaust conduit 27
between the stacks and the lower/inner side of the wall 127 and
then out through exhaust openings in the base plate 7. The hot
cathode exhaust stream exchanges heat with the air inlet stream
across the wall 127.
Thus, the module 1 of this embodiment may contain separate air and
fuel heat exchangers instead of the multi-stream heat exchanger 13.
The separate fuel heat exchanger (in which the fuel inlet stream
exchanges heat with the fuel exhaust stream) may be located in the
chamber 5 inside the base 3. The shell 11 containing the heat
exchanger 125 may be made by metal casting (i.e., cast as a single
unit) or other suitable methods. Heat exchanger 125 fins and flow
passages are incorporated into the casting process. Insulating
materials and other secondary materials or features are added after
the initial casting. The use of "cast in place" heat exchange
surfaces improves the heat transfer between the air inlet and
exhaust streams. Furthermore, a single component shell 11 improves
the serviceability of the system and may allow service in the field
rather than in a factory.
CVD Dielectric Coating.
In another embodiment, conduits such as air and fuel lines, and
metallic fuel manifold plates are electrically isolated using a
coated dielectric layer. Such layer may be deposited by any thin
film deposition method, such as chemical vapor deposition (CVD) or
physical vapor deposition, such as direct chemical vapor
deposition, physical vapor deposition, plasma enhanced chemical
vapor deposition or atomic layer deposition. Any suitable
dielectric layers materials may be used, such as silicon oxide,
silicon nitride, titanium oxide, titanium nitride, and aluminum
oxide.
For example, as shown in FIG. 12, the dielectric layer can be
coated on a flange joint. The joint is made using a glass material
to join the two coated metal flanges. For example, the dielectric
layer may be deposited upon the mating surfaces of the flange for
an electrically "live" fuel connection. As shown in FIG. 12 (which
is not drawn to scale to show the detail of the flange), the stacks
9 are arranged on the base plate 7. A fuel inlet line 29 provides
fuel into the stacks 9 either directly from below the base plate 7
or from outside the stacks via fuel feed plates 131 which are
described in U.S. application Ser. No. 11/276,717 filed Mar. 10,
2006 and incorporated herein by reference in its entirety. A flange
in the fuel inlet line may be positioned adjacent to a dielectric
compensator 134 described in U.S. application Ser. No. 11/436,537
filed May 19, 2006 and incorporated herein by reference in its
entirety, or in another location in the fuel inlet line 29. The
dielectric layers 135 are coated upon the flange members 133 of the
flange connection. The glass material 137 is located between the
dielectric layers 135.
In the case of some designs, perfect matching of thermal expansion
coefficient would not be required through the use of expansion
plumbing or bellows such as the compensator 134. In these cases,
the dielectric may be engineered to be very well adhered and rugged
on the surface of the flange.
Several methods may be used in order to ensure that dielectric
layer cracking does not adversely impact the device performance.
For example, multiple deposition steps may be used to deposit the
layer or alternating between two different dielectric material
deposition steps are used to reduce stresses. For example, a
dielectric film comprising alternating silicon oxide and silicon
nitride layers, such as a nitride layer between two oxide layers,
may be formed. The oxide layers tend to be low in residual stress
but have a lower toughness. The nitride layers are tougher but
include significant residual stress. By encapsulating the nitride
layer between the oxide layers, the tendency to form cracks is
reduced. If desired, the surface of the flange members 133 may be
roughened prior to the dielectric layer 135 deposition. This would
allow for more surface contact of the dielectric layer(s) 135. If
desired, a post deposition anneal may be performed to reduce
residual stresses in the layer(s) 135.
When the thermal expansion coefficient must be well matched, more
complex oxides could be deposited using direct deposition methods,
including atomic layer deposition if needed, in order to achieve a
layer of material whose expansion rate matches that of the
substrate material quite well.
In another embodiment, the deposited dielectric layer(s) are used
to reduce the weight or cost of the hot box construction. Rather
than forming walls or structural segments of the hot box (shell 11)
from expensive alloys, the walls are constructed of lower cost
materials, such as steel, etc. The lower cost material is then
coated with one or more dielectric layer(s) 135 to prevent material
attack and metal degradation. One significant concern is often
hydrogen embrittlement of metal. Nitride films, such as silicon or
titanium nitride, have a significant effect in blocking the
diffusion of hydrogen. Dielectric layers are also useful in
blocking oxygen penetration to a metal surface, thereby preventing
oxidation. The entire exposed surface of metal structural members
can be covered with the dielectric layers to reduce hydrogen or
oxygen penetration. The walls of the hot box are formed of a
combination of structural elements and thin walled sections. The
thin sections are thin metal sheets. These sheets are similarly
coated with deposited dielectric layers to prevent hydrogen
embrittlement or oxidation.
Internally Manifolded Interconnect.
In the embodiments shown above, the stacks comprising fuel cells
and interconnects are externally manifolded for air streams and
internally manifolded for fuel streams. However, in another
embodiment, the stacks are designed for internally manifolded fuel
and air flow streams. The flow paths maybe cross flow in nature
with interconnect design features included to allow for stack
assembly, and vertical mounting or horizontal mounting to a
vertical manifold as will be described below.
FIG. 13A illustrates one interconnect 201 design for use with a
full sized fuel cell electrolyte in which the electrolyte extends
to the outer extent of the interconnect. FIG. 13B shows how the
interconnect 201 is positioned with respect to the fuel cell
electrolyte 203. Each flow stream is self contained via a glass
seal and electrical isolation achieved by the electrolyte. Fuel and
air inlet and exhaust streams pass through the opposing openings
205 in the interconnect 201 and openings 207 in the electrolyte
203.
FIG. 14A illustrates an interconnect 211 for use with an
electrolyte that is smaller than the electrolyte. The electrolyte
213 is contained in a picture frame type recess one side of the
interconnect 211 as shown in FIG. 14B. The seals are achieved in
the same glass seal manner. Electrical isolation is achieved via
the glass seal layer. In this configuration, the interconnect 211
contains fuel and air flow openings 215 but the electrolyte 213
does not.
Side Mounted Stacks/Multilevel Radial System.
In another embodiment, the module is configured to facilitate the
ease of removal of the damaged stack. In this configuration, the
stacks are mounted not vertically as shown in FIGS. 1 and 2, but
horizontally (i.e., with the cell stacking direction extending
parallel to a horizontal axis) on central column 301 mounting
surface which extends perpendicular to the base plate 3, as shown
in FIGS. 15A-15C. FIG. 15A is a top view of the module. FIG. 15B is
a side view with the shell 11 removed. FIG. 15C is a three
dimensional perspective view of the shell 11 with the internal
components shown in dashed lines. The air heat exchanger and/or the
ATO may be incorporated into the central column 301. The stacks 9
have internal air and fuel manifolds and the gas feeds and exhausts
303 come from the central column 301 as shown in FIG. 15B. Each
stack column 9 is made up of the maximum height of stack that can
be fed from the base 3. This allows the removal of individual stack
columns as required without disturbing other stacks. The stack can
be designed such that they are positioned on ceramic or other
insulating rails 305 as shown in FIG. 15B. This allows for the
stacks 9 to be slid in and out of position easily. The stacks are
bolted in place, securing them to the central column. Vertical
support for the stacks can come in the form of ceramic spacer
wedges/pillows between one stack and its next vertical neighbor.
The shell 11 contains thermally insulated doors 302 which allow
access to the stacks 9.
In alternative embodiments, multiple rows of stacks (multiple
levels separated in a vertical direction) or stacked hot boxes are
provided, as shown in FIG. 15C. The plumbing (i.e., gas conduits)
can be provided in the base 3 so that all connections are at the
bottom. If desired, multiple bases 3A, 3B, 3C may be provided
between each level 311A, 311B of stacks 9. The fuel and/or air may
be fed into and removed from the bottom base of the module such
that the air and fuel streams serially travel through all of the
vertically separated levels 311 of the module. Alternatively, the
gas streams may be separately provided into and removed from each
level 311 of the module. For example, the streams may be provided
into and removed from each base 3A, 3B and 3C corresponding to each
level 311 of the stacks 9. The bases may contain heat exchanger(s)
and/or auxiliary reactors 10, 111 for each level 311. The stacks
can be made possibly in shorter columns to allow for more stacks in
a circle. Alternatively the radius of hot box can be increased to
accommodate more stacks in each horizontal level. Corners of the
system are available for plumbing to connect to units above or
below (for hot box stacks) and for air or fuel connections or
exhausts 313, as shown in FIG. 15D. The stacks 9 may be oriented
horizontally in each level, as shown in level 311B in FIG. 15C
and/or the stacks 9 may be oriented vertically in each level, as
shown in level 311A.
The fuel cell systems described herein may have other embodiments
and configurations, as desired. Other components may be added if
desired, as described, for example, in U.S. application Ser. No.
10/300,021, filed on Nov. 20, 2002, in U.S. application Ser. No.
11/656,006 filed on Jan. 22, 2007, in U.S. Provisional Application
Ser. No. 60/461,190, filed on Apr. 9, 2003, and in U.S. application
Ser. No. 10/446,704, filed on May 29, 2003 all incorporated herein
by reference in their entirety. Furthermore, it should be
understood that any system element or method step described in any
embodiment and/or illustrated in any figure herein may also be used
in systems and/or methods of other suitable embodiments described
above, even if such use is not expressly described.
The foregoing description of the invention has been presented for
purposes of illustration and description. It is not intended to be
exhaustive or to limit the invention to the precise form disclosed,
and modifications and variations are possible in light of the above
teachings or may be acquired from practice of the invention. The
description was chosen in order to explain the principles of the
invention and its practical application. It is intended that the
scope of the invention be defined by the claims appended hereto,
and their equivalents.
* * * * *
References